The objective of this proposal is to coagulate experimental arterial aneurysms while preserving the patency of the parent artery, using laser energy. An optical fiber within an arterial catheter will be employed to direct a laser beam into an aneurysm sac from inside the arterial system. The variables of laser power and exposure will be studied to determine the range necessary for aneurysm ablation. The animal model will consist of a series of rabbits in which an experimental pouch aneurysm is created on the side of the common carotid artery. Following angiographic demonstration of a patent well-formed aneurysm, each aneurysm will be treated with a laser. An optical fiber, to which a laser is coupled, will be introduced into the carotid artery until its tip is adjacent to the aneurysm orifice. Since the aneurysm will be at right angles to the lumen of the artery, the fiber tip will be optically constructed to reflect the laser beam sideways into the aneurysm. The experimental aneurysm will be observed under direct vision during treatment to determine the moment of aneurysm closure or ablation. Angiography will be used to confirm closure of the aneurysm and patency of the parent carotid artery. Following treatment, the rabbits will be followed clinically and studied angiographically at intermittent intervals for six months. To determine the effect of therapy on the aneurysm, the parent vessel and adjacent tissues, all the animals will be sacrificed and studied pathologically including those that may die before sacrifice. Tissues distal to the surgical site such as the intracranial circulation and the brain will be examined for ischemia and/or infarction secondary to vasospasm, embolus or thrombosis. The anticipated goal of these experimental studies is to apply this method of therapy for the treatment of human intracranial aneurysms. This approach would be particularly useful in treating intracranial aneurysms which are unamenable to surgery, such as those arising from the basilar and vertebral arteries.